Home > XF-91 Thunderceptor

The Republic XF-91 Thunderceptor was an mixed-propulsion interceptor using a jet engine for most flight, and a cluster of four small rocket engines for added thrust during climb and interception. The design was largely obsolete by the time it was completed due to the rapidly increasing performance of contemporary jet engines, and was built to the extent of two prototypes only. One of these was the first US fighter to exceed Mach 1 in level flight.

The Thunderceptor design was one of two swept-wing modifications based on the original F-84 Thunderjet, the other being the F-84F Thunderstreak which happened later. A serious problem with most swept wing designs of the era was dangerous performance at low speeds and high angle of attack. At low speeds airflow over the wing tended to "slide" towards the wingtip, which caused it to stall before the rest of the wing. In this situation the lift from the wing would start moving forward, pitching the nose up and leading to an even greater angle of attack. Planes caught in this regime would often stall and crash, and a rash of such accidents on the F-86 Sabre led to the term Sabre dance.

The Thunderceptor's most notable design feature was intended to address this problem. The wings were built to have considerably more chord (distance from front to back) at the tip than root, allowing them to generate more lift. This neatly addressed the problems with Sabre dance by delaying the point of stall on the tip to that of the entire wing. A side effect of this design was that the tips had more internal room, so the landing gear was mounted to retract outward with the wheels lying in the wingtips, using two small tires instead of one larger one. Another design change was the ability to vary the angle of incidence of the wing as a whole, tilting it up for low speed operations during takeoff and landing, and then "leveling it off" for high-speed flight and cruise. This allowed the fuselage to remain closer to level while landing, greatly improving visibility.

In keeping with its intended role as an interceptor, the nose was redesigned to incorporate radar, forcing them to move the air intake for the engine from its original nose-mounted position to a new intake below it. The fuselage was otherwise very similar to the F-84's. The first prototype did not include the radome, although this was a part of the second prototype.

The first prototype made its first flight on May 9May 9 is the 129th day of the year in the Gregorian Calendar (130th in leap years). There are 236 days remaining. Events 328 Athanasius elected bishop of Alexandria. 1092 Lincoln Cathedral is consecrated. 1429 Joan of Arc defeats the English troops besieg, 19491949 is the common year starting on Saturday. see link for calendar) Events January-February January 4 RMS Caronia of the Cunard Line departs Southampton for New York on her maiden voyage January 4 February 22 Series of winter storms in Nebraska, Wyoming,, breaking the speed of sound in December 1951. It was later modified with a small radome for gunnery ranging (although not the "full" radome from the second prototype). The second prototype included the full radome and chin-mounted intake, but was otherwise similar. This airframe was later modified to use a V-tailIn aircraft, a V-tail (sometimes called a "butterfly tail") is an unconventional arrangement of the tail control surfaces that replaces the traditional fin and horizontal surfaces with two surfaces set in a V-shaped configuration when viewed from the fron for testing. With both the jet and rockets running, the plane could reach Mach 1.71, rather respectable for the early 1950sCenturies: 19th century 20th century 21st century Decades: 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s 2000s Years: 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 Events and trends Technology United States tests the first fusion bomb.. Both prototypes were used for testing for several years.

As an interceptor the Thunderceptor was soon eclipsed by designs from other companies, but like the Thunderceptor none of these would go into production. The US Air Force decided to wait the short time needed to introduce newer and much more capable designs created as a part of the 1954 Interceptor project. The Thunderceptor, like the other interceptor designs of the era, had extremely short flight times on the order of 25 minutes, making them almost useless for protecting an area as large as the United States. The 1954Events January events January 14 The Hudson Motor Car Company merges with Nash-Kelvinator forming the American Motors Corporation January 14 Marilyn Monroe weds Joe DiMaggio. January 15 Mau Mau leader Waruhiu Itote is captured in Kenya January 20 The Nati designs outperformed the F-91 in speed, range, loiter time, and included the radar and fire control systems needed for night and all-weather operation. The era of the dedicated day fighterA day fighter is a fighter aircraft equipped only to fight during the day. More specifically it is typically used to refer to a multi-purpose aircraft that does not include equipment for fighting at night, although it is sometimes used to refer to some in-type interceptor were over.